1. Field of the Invention
The present invention relates to a lining material for pipe lines, chiefly those buried in the ground, such as sewage pipes, which is capable of forming as a lining thereof a strong inner pipe made of fabric-fiber-reinforced plastic for reinforcing the pipe lines and to a process for providing the pipe lines with such fabric-fiber-reinforced plastic lining. More particularly, the present invention relates to a lining material for pipe lines already constructed and buried in the ground, such as gas pipe lines, city water pipe lines and sewage pipes, for the purpose of repair or reinforcement of these pipe lines, which comprises a plastic tubular film overlaid with a specific fabric-fiber mat impregnated with a hardenable resin and an outer film, and to a process for providing the pipe lines with such fabric-fiber-reinforced plastic lining, which comprises inserting the lining material into the pipe lines, applying the lining material onto the inner surface of the pipe lines under internal pressure exerted by a pressurized fluid introduced into the pipe line and curing the resin by heating.
2. Description of the Prior Art
From the past, various lining materials are known for repair or reinforcement of pipe lines. In particular, a lining material comprised of a mat of a fibrous material impregnated with a hardenable resin is known, for example, in Japanese Patent Publn. Nos. Sho. 51-40595 and 58-9317. The lining material disclosed in Japanese Patent Publn. No. Sho. 51-40595 (referred to hereinafter simply as Ref. 1) comprises, as shown in FIGS. 1-5 and 8, a mat or tubular mat of a strong fibrous material such as glass fibers impregnated with a liquid thermohardenable resin being interposed, like a sandwich between an inner tubular plastic film and an outer plastic film. On application of this lining material onto the inner surface of pipe lines, the lining material is introduced into the pipe lines after peeling off the outer plastic film and is inflated so as to be brought into intimate contact with the inner surface of the pipe line, and the thermohardenable resin is cured to form a fiber-reinforced plastic (FRP) lining on the inner surface of the pipe lines. The inner tubular plastic film may be removed by peeling after completion of the FRP lining (Col.12, lines 2-4, Ref. 1).
A mat or tubular mat of a strong fibrous material impregnated with a liquid thermohardenable resin, which is usually interposed between inner and outer plastic films and is heated under a given condition to thicken the liquid resin, is called according to ASTM "Sheet Molding Compound" (referred to hereinafter as SMC). In this case, two plastic films on both sides of the resinimpregnated mat which will form FRP serve to prevent evaporation of the hardenable resin ingredient in the mat, for example, monomeric styrene.
In the lining material disclosed in Ref. 1, a mat of glass fibers is firstly spread on a plastic film capable of easily being split off and is impregnated with a hardenable resin to form a curable FRP, i.e. FRP not yet cured which is then overlaid with a tubular film as shown in FIG. 2. Both ends of the curable FRP are folded on the tubular film so that it may be wrapped with the curable FRP in such manner that both lateral end portions of the curable FRP are overlapped (FIG. 4). The curable FRP in the form of a tube is then wrapped with the outer plastic film and a composite tube thus obtained is finally heated to thicken the curable FRP whereby a tubular SMC is obtained (FIG. 5).
However, the lining material of Ref. 1 has such a drawback that when it is inserted into the pipe lines, a strong force is exerted to SMC due to frictional resistance against the inner surface of the pipe lines and so the SMC is locally stretched to reduce its thickness or is broken down in the extreme case. In particular, SMC in a not-yet-cured state is poor in tensile strength and easily undergoes deformation.
It is also drawback of SMC that it has no stretchability. Upon application of the the lining material, it is usually so adjusted that its outer circumferential length is approximately identical with the inner circumferential length of the pipe line to be treated. When the lining material inserted into the pipe line is inflated to bring the lining material into intimate contact with the inner surface of the pipe line evenly, however, the whole parts of the outer of the lining material are not always contacted to the correct position of the inner surface of the pipe line even if the lining material is uniformly inflated. The part of the lining material initially contacted with the inner surface of the pipe line is not slidable to the correct position due to frictional resistance so that the lining material may form wrinkles due to distortion and occurrence of locally loose portions. On the other hand, the portion of the lining material not finally attached to the inner surface of the pipe line is strongly elongated so that the weak portion of the lining material tends to be broken down as SMC has no stretchability.
The lining material disclosed in Japanese Patent Publn. No. Sho. 58-9317 (referred to hereinafter as Ref. 2) comprises SMC interposed, like a sandwich structure, between an outer tubular film and a specific inner tubular film having an outer layer capable of being easily split off from SMC and an inner layer having a high moisture-proof property. Ref. 2 discloses as a specific example of the inner tubular film one having an outer layer of polyamide, polyester or a fluorine resin and having an inner layer of polyvinyl chloride, polyester, polyolefin or a fluorine resin, one having an outer layer of polyamide and an inner layer of polyolefin (Col. 2-3, Ref. 2) and particularly one having an outer layer of nylon 6 film and an inner layer of a laminated film of nylon 6 and polyethylene (Table 4).
What is taught by Ref. 1 and Ref. 2 is that SMC is suitable as a material for lining pipe lines and is converted at the final stage to FRP although there are some differences between both in the structure of the inner plastic film. Accordingly, the nature and structure of SMC of these Refs. 1 and 2 applied onto the inner surface of pipe lines are the same. In these known arts, the lining material is commonly applied onto the inner surface of pipe lines in such a manner that SMC is inserted after peeling off the outer plastic film into a pipe line and inflated so as to be brought into contact evenly with the inner surface of the pipe line, and then SMC is cured by heating with steam or hot blast. The inner tubular film is then peeled off from the resultant FRP as shown in FIG. 10 of Ref. 2. If the inner surface of the pipe line is wetted by underground water intruded thereinto through any superannuated or damaged portion, SMC will not be completely cured in the presence of such water. As the purpose of applying the lining material to pipe lines resides originally in repairing or reinforcing such damaged or superannuated portions of the pipe lines, the above result would not achieve the inherent purpose of pipe-lining. On the other hand, SMC can be prevented from contact with water by effecting the pipe lining without peeling off the outer plastic film covering SMC. In this case, the contact of SMC with water can certainly be prevented but solvents contained in SMC remain without being evaporated which disturb the formation of a strong lining material.
In general, a mat of glass fibers impregnated with a liquid unsaturated polyester resin which is then somewhat thickened by effecting partial polymerization under heating is used as SMC. The liquid unsaturated polyester resin usually contains a large amount of styrene as reactive solvent which is partially polymerized by way of crosslinking to the polyester chain. As the amount of styrene is excess for the crosslinking to the polyester chain, such excess styrene evaporates while curing of SMC takes place and a rigid FRP is obtained. In case the outer plastic film is not removed of curing of SMC, however, the evaporation of excess styrene is inhibited so that a considerable amount of styrene remains on conversion of SMC into FRP. Accordingly, the resultant FRP becomes so soft that it may easily be scratched by nails. Such a soft FRP is not suited as the lining for pipe lines.
In case SMC is molded by pressing, such molding is generally conducted at a temperature of 130.degree.-150.degree. C. under pressure of 30-80 kg/cm.sup.2 whereby the glass fibers can completely be impregnated with the resin and any optional filler. In case of curing SMC in Ref. 1 or 2, however, the lining material is internally pressed against the inner surface of the pipe line by pressurized fluid such as the hot blast or steam as heating source. Accordingly, the curing of SMC in this case is conducted at a mild condition involving a temperature of 60.degree.-80.degree. C. and a pressure of 1 kg/cm.sup.2. Thus, the glass fibers cannot sufficiently be impregnated with the resin and any optional filter and the cured resin tends to form interstices through which water oozes out if the external water pressure is high.
In case a laminated film of a polyamide and polyethylene is used as inner layer in the lining material of Ref. 2, the polyethylene film which is poor in heat-resistance may be molten when heated steam is introduced as the heating medium for curing SMC. In this case, there is a fear that the steam can penetrate the polyamide film and disturb the curing of unsaturated polyester in SMC. Accordingly, polypropylene film possessing a higher heat-resistance may be used in place of polyethylene film, but polypropylene exhibits a high rate of contraction on heating and high tensile elasticity with low tear resistance, thus resulting in that the polypropylene film is shrunk by the heat of steam and is easily torn to permit permeation of steam which disturbs the curing of unsaturated polyester resin. Furthermore, in case nylon 6 is used as an outer layer of the tubular film, this nylon 6, having a relatively low melting point, may be partially molten when the temperature is maintained at about 200.degree. C. for several minutes for the curing of unsaturated polyester resin in FRP. In this case, the molten nylon 6 can no longer be peeled off and the inner surface of the resultant FRP becomes uneven.
In general, a lining material for pipe lines is desirably provided on the inner surface thereof with an air-tight coating of a resin to impart a water-proof property to the lining material. In this case, however, heating of the lining material is often necessary for integrally combining the air-tight coating layer with the lining material. In case SMC is used in the lining material, there is a detriment such that SMC is cured by such heating prior to being applied to pipe lines.
Thus, the prior art lining materials of SMC type have, as having been discussed heretofore, a number of disadvantages to be overcome. In the above circumstances, there is a great demand for developing a new type of lining material for pipe lines in place of the conventional lining materials of SMC type having a number of drawbacks.